Urine sediment analysis is one of the most commonly performed diagnostic tests for providing an overview of a patient's health status. A urine sample can be obtained from a patient's body and stored in a test tube for later processing and analysis. The appearance of certain characteristic sediments also called formed elements in a urine sample may be clinically significant and/or be indicative of pathological conditions in a subject.
Generally, abnormal urine may contain a variety of formed elements, such as blood cells, epithelial cells, crystals, casts, or microorganisms. For example, urine samples may contain cells of hematological origin. Erythrocytes or red blood cells (RBCs) may be present in the urine as a result of bleeding (hematuria) at any point in the urogenital system from the glomerulus to the urethra. The presence of leukocytes or WBCs, neutrophils, eosinophils may have clinical significance. Glitter cells are a type of neutrophil seen in hypotonic urine of specific gravity 1.010 or less. The presence of lymphocytes has been used as an early indicator of renal rejection after transplant. Eosinophils are associated with drug-induced interstitial nephritis, Mucus threads originating from the kidney or the lower urinary tract can be present.
Urine samples may also contain cells of epithelial origin. A few renal epithelial cells also called renal tubular cells, may be found in the urine of healthy persons because of normal exfoliation. However, the presence of excessive renal tubular cells is indicative of active renal disease or tubular injury. Of the various types of epithelial cells found in urine (renal, transitional or urothelial, and squamous), renal epithelial cells are the most significant clinically. They are associated with acute tubular necrosis, viral infections (such as cytomegalovirus), and renal transplant rejection. Their presence is also increased with fever, chemical toxins, drugs (especially aspirin), heavy metals, inflammation, infection, and neoplasms. Moreover, the presence of inclusion bodies may be seen in viral infections, such as rubella and herpes, and especially with cytomegalovirus.
Urine can also contain transitional epithelial cells or urothelial cells. Transitional epithelial cells are the multilayer of epithelial cells that line the urinary tract from the renal pelvis to the distal part of the male urethra and to the base of the bladder (trigone) in females. They may be difficult to distinguish from renal epithelial cells, but they are generally larger and more spherical. A few transitional cells are present in the urine of healthy persons. Increased numbers are associated with infection. Large clumps or sheets of these cells may be seen with transitional cell carcinoma.
Urine can also contain squamous epithelial cells. Squamous epithelial cells line the urethra in females and the distal portion of the male urethra. The presence of large numbers of squamous cells in females generally indicates vaginal contamination.
Urine can also contain clue cells. Clue cells are another type of squamous cell of vaginal origin, may be seen contaminating the urine sediment. This squamous epithelial cell is covered or encrusted with a bacterium, Gardnerella vaginalis, whose presence is indicative of a bacterial vaginitis.
Urine can also contain oval fat bodies, renal tubular fat, or renal tubular fat bodies. These bodies are renal epithelial cells (or macrophages) that have filled with fat or lipid droplets. The fat may be either neutral fat (triglyceride) or cholesterol; they have the same significance clinically. Presence of oval fat bodies in urine is indicative of disease abnormality and should not be overlooked. They are often seen with fatty casts and fat droplets in the urine sediment and are associated with massive proteinuria as seen in nephrotic syndrome.
Urine can also contain microorganisms such as bacteria and yeast. Normally, urine is sterile, or free of bacteria. However, certain bacteria are typically seen in urine of an alkaline pH. Associated sediment findings may include the presence of WBCs (neutrophils) and casts (WBC, cellular, granular, or bacterial). Although infections are most often due to gram-negative rods of enteric origin, infectious organisms may also be gram-positive cocci.
In addition, yeast may be seen in urine, especially as the result of vaginal contamination such as contamination from female patients with yeast infections. It is also associated with diabetes mellitus owing to the presence of urinary glucose. Yeast is a common contaminant, from skin and the environment, and infections are a problem in debilitated and immunosuppressed or immunocompromised patients.
Traditionally, analysis of sediments in urine has been performed by visual inspection using a microscope in a general laboratory. With these approaches, a urine sample is first subjected to centrifugal separation and enriched. Sediments thus obtained are in some cases stained and then loaded on a microscope slide, and are subjected to manual determination and counting under the microscope.
Sample preparation steps can include concentration of the urine sediments by centrifugation and sometimes application of a microscopy stain to enhance contrast, e.g., between sediment types such as RBCs, WBCs, and epithelial cells. In a manual count, the technician views the wet mount slide, distinguishing among types of visible cells or by their appearance using professional judgment, and manually counts the number of observed urine sediment of different types within a predetermined area.
Various stains have been used to stain cells or cellular structures found in urine samples. For example, Wright's stain is a stain that has been used to stain urine samples for examination under a light microscope. Staining a urine sample involves the use of multiple solutions and steps in proper order to ensure the staining agent is correctly applied and the cell structure is appropriately preserved. A fixing agent can be applied to the sample in a first step to preserve the sample from degredation and maintain the cell structure. Afterwards, a permeabilizing agent can be applied to the sample in a second step to dissolve cell membranes in order to allow the staining agent to enter the cells. The staining agent can be applied to the sample in a third step to stain the appropriate structures. The sample may be further rinsed for observation, or additional steps may be taken to apply additional stains, counterstains, or other perform other actions.
It is important to perform the steps in the appropriate order for the appropriate amounts of time. If the sample is permeabilized before being fixed, the cell structures in the sample can be degraded prior to being fixed and any ability to discern the original cellular morphology is lost. Additionally, the staining cannot occur prior to the permeabilizing step, or the staining agent will not properly penetrate the cells and stain the structures within the cells. Additionally, if any of the steps, such as fixing, permeabilizing, and staining, are performed too rapidly, the cell's morpohology may be lost and/or the cell and its internal structures may not be properly stained. Also, the use of pH modifiers may be necessary prior to other steps in order to ensure proper functionality of components that cannot function properly in the urine natural pH. Current staining techniques require multiple steps and significant time.
Current staining techniques require dilution of samples in the contrast agents generally around 9 parts contrast agent to 1 part sample. It can be undesirable to have large-volume mixtures for use with image-based analysis systems such as flow cytometery systems, at least because of the time it takes to process a volume of a mixture.
Automated analyzers are becoming more prevalent. The use of systems for urine analysis is generally described in U.S. Pat. No. 4,473,530 to Villa-Real, entitled “Compact Sanitary Urinalysis Unit”; U.S. Pat. No. 3,894,845, entitled “Urine Collection and Analysis Device” and U.S. Pat. No. 3,988,209, entitled “Microorganism Analysis Device”, both to McDonald; U.S. Pat. No. 4,973,450 to Schluter, entitled “Device for Urinalysis”; U.S. Pat. No. 4,622,298 to Mansour, et al., entitled “Detection and Quantitation of Microorganisms, Leukocytes and Squamous Epithelial Cells in Urine”; and U.S. Pat. No. 5,132,232 to Parker, entitled “Method and Apparatus for Preparation of Liquids for Examination.” U.S. Pat. No. 4,612,614 to Deindoerfer, et al., entitled “Method of Analyzing Particles in a Fluid Sample”, reports a method for analyzing urinary sediments by distributing a sample over an extended area, such as a microscope slide or a flow cell. Deindoerfer, et al. reports the use of a plurality of optical still images of the sample that are converted into electronic images which are displayed in an array ordered by classes of visually discernable characteristics. However, many of these earlier developed urine analysis systems generally lacked the throughput, the accuracy, and/or the general applicability required for adaptation across all targets/subjects for all intended purposes.
For automation of urinary sediment determination, an automated flow microscope may be used (e.g., flow-type automatic microscope—iQ® 200, Iris Diagnostics). With these types of devices, a urine sample is introduced to a flat type flow cell without pre-concentration and images are taken and stored while the sample is flowing through the flow cell. However, urinary sediments are diversified in their morphology and many sediments are being damaged, and therefore, determination of images taken with good accuracy are difficult to achieve. It is particularly difficult to determine small-sized sediments, such as erythrocytes (especially dysmorphic erythrocytes), bacteria and crystals with good accuracy without external user validation.
The various automated systems described above rely on rapid analysis of samples. The number of and duration of the steps of the staining process can be a limiting factor in the speed and efficacy of automated particle analysis systems. Automated particle analysis systems can be more efficient if the staining process is shortened, and further more efficient if the staining process is performed in a single step. Additionally, the automated particle analysis systems can be more efficient if the total size of the sample is kept to a minimum.